ADVANCES IN MODEL CONSTRUCTION OF ANEMOCHORIC SEED LONG-DISTANCE DISPERSAL

Abstract

Long-distance dispersal (LDD) of plant propagules has significant ecological and evolutionary implications for plant species migrations, biological invasions, conservation biology and many other fields of research. Although seeds can disperse by many different processes, the seeds of many herbaceous species of open grasslands and tree species in temperate and tropic zones are anemochoric, i. e., wind dispersed. Modeling the dispersal of anemochoric seeds, particularly their long distance dispersal, is a major research field because of the importance of this ecological process for understanding such phenomena as the spread of invasive alien plants and gene flow among meta-populations in fragmented landscapes. Our search results indicated that there are no synthesis papers on the LDD of anemochoric seeds. This paper discusses the background and significance of long-distance dispersal of air-borne seeds, analyzes the basic formulas and structures of models of seed dispersal by wind, summarizes recent advances in phenomenological and mechanistic models, and presents future research directions in this field. LDD models of anemochoric seeds are categorized into two major classes : phenomenological models and mechanistic models. Phenomenological models include short-tailed dispersal kernels (SDK), Leptokurtic fat-tailed kernels (LFK) and mixed dispersal kernels (MDK). The LFK and MDK models are most promising for simulating long-distance dispersal of seeds. Mechanical models are categorized into Eulerian advection-diffusion models (EADM) and Lagrangian stochastic models (LSM). The mechanisms of LDD and the major parameters of these two classes of models are a major focus of this paper. Important mechanisms of LDD include synchronization of seed release with suitable weather conditions. and updrafts that occur at forest edges and on the ground surface. Also, gradients of wind speed that form during storms was speculated as being an important mechanism of LDD. Operative factors in wind LDD models include biological, meteorological and topographical factors. We introduce and evaluate a number of models that have been used successfully to model LDD by wind, including tilted plumed model (TPM), advection-diffusion-deposition model (ADDM), no-shelter model (NSM), background model (BM), WINDISPER, modified WINDISPER (MWINDISPER) and PAPPUS. Lastly, the current status of wind LDD model construction is analyzed and some gaps are pointed out. The authors advocate that more effort should be made to construct models for herbaceous species since currently there are many more wind LDD models for tree species. There are many challenges and needs for modelers to link models with empirical field data of fragmented landscapes. Finally, collaborative approaches among researches from different fields are encouraged in order to improve LDD model forecasting especially with regard to increasing the precision of inputs of attributes of the physical environment